1. Field of the Invention
The invention relates generally to testing of electronic systems, such as system-on-chip semiconductor devices.
2. Related Art
Automatic test equipment (referred to generally as a “tester”) is known for testing many types of electronic devices under test (DUTs). For example, testers for test printed circuit boards and semiconductor devices are known.
In some scenarios, testers are used during manufacture of the electronic devices. In this capacity, the testers are used to identify defects such that the results of testing can be used to impact the manufacture of a DUT by conditioning certain operations on the results of testing. For example, manufacturing steps that result in the device being packaged and shipped to a customer are typically performed only if testing on a device indicates that the device is working properly. If such tests indicate that the device is not working properly, the device is often diverted such that different operations to rework or scrap the device are performed.
Testers are typically configured to run test scenarios that emulate various real-world conditions that a DUT might experience in operation. Each test scenario, for example, may have a sequence of steps that activate or utilize different portions of the DUT that are involved in a particular usage scenario. The collection of test scenarios may be selected to ascertain whether all portions of the DUT have been manufactured correctly.
The tester may implement such test scenarios by executing one or more test programs. The test programs specify operations to be performed by the tester to generate stimulus signals and measure responses for comparison to a response expected from a properly operating device. Execution of a test program may entail application of a “test pattern” to control the circuitry that generates or measures digital signals at numerous test points connected to a DUT. The test pattern is a fixed binary data set indicating, for each of multiple successive tester cycles, whether an instrument in the tester is to generate or measure a test signal. The pattern may also indicate other information about the test signals, such as their digital values.
Testers are also used while a product device is being developed—test chip to validate specific product features. During development, a design engineer may use a tester to execute test programs. These test programs are designed to exercise portions of the DUT, and are often written to surface design flaws in the DUT. Test programs created for this purpose may be limited to testing small portions of the DUT at a time.
Often, the development process is iterative, with an engineer, whether developing the DUT or the test program creating a test program and then loading that test program into a tester. The test program may be executed with a DUT connected to the tester. Based on the results of executing the test program, changes may be made to the design of the DUT. Though, changes to the test program may also result. Changes may be made, for example, to address initial flaws in the test program or as part of an incremental design approach in which, once portions of the test program or DUT are validated, other portions that interact with those portions may be added.
As the test program is changed, it may be reloaded into the tester and further iterations of the process of executing the test program, evaluating the results, and modifying the test program may be performed. These iterations can be compounded if, during testing, a problem with the design of the DUT is identified, requiring changes to the design.
A test system might also be used after a device has been manufactured. For example, if multiple devices that have been manufactured and put into use are experience similar defects, a manufacturer of the device may want to test samples to determine whether the failures are related to a latent defect in the design or systemic defects in the manufacture of the devices. Such testing may also be performed by developing a test program, possibly iteratively, to identify the source of the defects.